Electrical wave-guide system for producing a phase difference between two output waves and devices containing such a wave-guide system



, March 5, 1957 J. VAN DE LINDT 2,784,380

W. ELECTRICAL WAVE-GUIDE SYSTEM FOR PRODUCING A PHASE DIFFERENCE BETWEEN TWO OUTPUT WAVES AND DEVICES CONTAINING SUCH A WAVE-GUIDE SYSTEM Filed April 5, 1952 Willem Jocobus van de Lindt AGENT United States PatentC) ELECTRICAL WAVE-GUIDE SYSTEM FOR PRO- DUCING A PHASE DIFFERENCE BETWEEN TWO OUTPUT WAVES AND DEVICES CONTAIN- lNG SUCH A WAVE-GUIDE SYSTEM Willem Jacobus van de Lindt, Eindhoven, Netherlands,

assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee This invention-relates to electrical wave-guide systems for producing a phase difference between two output waves and to devices comprising such a wave-guide systern.

The invention is based on such a system formed by two wave-guides, of which the first has a length k and a rectangular sectional area having a long side a and a short side b and the second has a length l, differing from k and a rectangular sectional area having a long side and a short side d, waves having equal phases being supplied to the wave-guides on the input side thereof and the output waves being taken from the output side thereof. The wave-guide system according to the invent-ion is characterized in that the values of a and 0, both on the input side and on the output side of the wave-guide concerned are equal to an, whilst a and c for at least one of the waveguides between the input and the output have extreme values, aao and cao respectively being small with respect to an and in that O1O2 3a0(kl), where In order that the invention may be readily carried into effect, an example will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 shows a known wave-guide system;

Fig. 3 shows a wave-guide system according to the invention and Fig. 2 is a graph, with reference to which the operations of the wave-guide systems shown in Figs. 1 and 3 will be compared with one another.

It occurs in the waveguide technique that a definite phase displacement between two waves is desired, for example, in a push-pull crystal modulator the phase dilIerence is required to be 180 and in a push-pull TR-switch 90. It is known that any phase difference can be pr0- duced with the use of the wave-guide system shown in Fig. 1.

This system comprises the wave guides 1 and 2. The wave guide 1 has a length k and a rectangular sectional area having a long side no and a short side b. The wave guide 2 has a length l and a rectangular sectional area h-aving a long side an and a short side :2. The two wave-guides have a constant sectional area. Such rectangular waveguides are, in general, used for waves having a length A, of which the frequency is comparatively little in excess of the lowest critical frequency. These waves are of the type H10, where a so-called TE kind of oscillation occurs. More particularly, A is chosen to be such that waves of other kinds of oscillation do not occur. This is the case when a0 2ao. In the wave-guide occurs a wave having a length of A which, as is known, is not equal to A, but is 2,784,380 C Fatehted, s. 1 57 If waves of equal phases are supplied to the input sides 3 and 4 of the wave guides 1 and 2, waves having a definite phase difference can be taken fromthe output sides 5 and 6 of these wave guides. It is simply evident that Consequently, by correct choice of k and 1, any desired phase displacement may be obtained.

It is often desired that the phase displacement should not vary with the frequency or the wave length. In the push-pull crystal modulator, for example, a constant phase displacement of 180 is required for a definite frequency range. It is obvious that the system shown in Fig. 1 does notfulfill this requirement, since it follows from (1) and (2) that, if A varies, also A and hence will vary. This is the situation indicated by the line A of Fig. 2.

By way of example a system has been chosen, for which a0=2.29 cms., kl being equal to 1.19 ems. For a wavelength \=3.32 cms. ()t =4.76 cms.) a phase displacement of consequently occurs. For higher values of and A is lower and conversely, as is indicated by the line A.

In the wave-guide system according to the invention, shown in Fig. 3, this disadvantage is obviated. Corresponding parts are designated by the same references. The two wave-guides have near the ends a width an. The width a of the wave-guide 1 exhibits, as a function of the length co-ordinate s a maximum between the ends, whereas 'the width c of the wave-guide 2 exhibits a minimum as a function of s.

his now found that the phase displacement s, which occurs here between the waves taken from the output sides 5 and 6, if waves having equal phases are supplied to the input sides 3 and 4, no longer varies with the wavelength in a definite wavelength range. This wavelength range will lie in the aforesaid range, where ao 2ao and hence be serviceable in this system, if

It is found that 01 and 02 have a simple geometrical function. They indicate the magnification of the upper surface of the wave-guide, which is due to the fact that the width is not constant. Thus, for the wave-guide 1, O1 is equal to the sum of the cross-hatched surfaces 7 and 8, for the wave-guide 2 the sum of the cross-hatched surfaces '9 and 10 is equal to -02. The sign is due to the fact that in this case the upper surfaceh-as become smaller than it would be with a constant width as.

The centre of the wavelength range, in which 5 does substantially not vary with the wavelength, appears to lie where 3 Consequently, if-a phase displacement of a whole multiple (n) of 90 which will often occur,

must therefore be substantially a whole numeral.

From the Formulas 4 and 5 it follows, moreover, that k-l must be chosen to be such that Icl i In the Wave guide system according to the invention half of the phase displacement may, consequently, be understood to be produced by the difference in length kl in itself and the other half by the effect of the width variations themselves.

For the case ao=2.29 cms., Fig. 2 shows the variation of q& as a function of h and k for the wave-guide system according to the invention. Here the centre of the range in which substantially does not vary, lies near =4-.7 6 cms. This variation, which is indicated by the line B, is substantially fiat, which means that is substantially independent in this case of A and k and remains substantially 90'.

One of the surfaces 01 and 02 may be zero, without any objection. This means that one of the two wave guides 1 and 2 may have a constant width as. It should be noted that the dimensions b and d need fulfill only the normal requirements for waveguides.

In Fig. 3 the width variations are shown on an exaggerated scale for the sake of clearness.

It will be obvious that, where reference has been made in the foregoing to width, this term is to be understood to mean the efiective width, so that all measures liable to 'aifect the width may be used within the scope of the invention to obtain the width variations.

What I claim is:

1. An electrical wave-guide system for producing a phase difference between two output waves, comprising two wave-guides, of which the first has a length k and a rectangular sectional area having a long side a and a short side b and the second a length l, differing from k, and a rectangular sectional area having a long side c and a short side d, and means to apply an input wave cophasally to said two wave-guides at the input ends thereof and whereby the output waves displaced in phase are taken from the output ends thereof, characterized in that the values a and c, both at the input and at the output end ofthe waveguide concerned, are equal to a0, while a and c for at least one of the wave-guides have extreme values differing from at) between the input and the output, aao and cao respectively being small with respect to an and in that ar-mat t= and A is the wavelength of operation.

2. A wave-guide system, as claimed in claim 1, characterized in that the value of is at least substantially equal to a whole numeral.

References Cited in the file of this patent UNITED STATES PATENTS 

